This relates generally to imaging systems and, more particularly, to simultaneously operating two-dimensional arrays or blocks of image pixels on an image sensor.
Modern electronic devices such as cellular telephones, cameras, and computers often include camera modules having digital image sensors. An image sensor (sometimes referred to as an imager) is formed from a two-dimensional array of image sensing pixels. Each pixel receives incident photons (light) and converts the photons into electrical signals.
Capturing images using a CMOS image sensor typically involves using an electronic rolling shutter (ERS) algorithm to successively reset, integrate, and read out single rows of image pixels on the image sensor. In the traditional ERS algorithm, row reset and readout are typically performed for a single row at a given time. Row reset refers to an operation which prepares a pixel for light capture by resetting a charge storage node to a given voltage. Row readout refers to an operation on image pixels that have been exposed to light for a desired duration of time, that involves sampling the pixel columns of a given row and converting a value related to the amount of charge stored by the pixel during exposure to a digital signal.
Traditional image sensors that are operated using an ERS algorithm typically have pixel output stages for only a single row of pixels. The delay associated with processing signals for a single row through the pixel output stage often determines the maximum frame rate and resolution at which a given image sensor can be configured to operate.
Another parameter that often determines the maximum frame rate and resolution at which a given image sensor can operate is row integration period. This integration period specifies the duration during which charge associated with incident light is allowed to be accumulated in a given pixel before the charge is read out. When row readout speeds are constant, but higher frame rates are desired or required, an image sensor will be forced to reduce exposure or integration period of pixels in its rows, which can lead to poor image capture in low-light environments or a reduced resolution image.
Row read-out is traditionally performed in a pixel output stage which provides a processing data-path (such as sample-and-hold, amplification, analog-to-digital conversion, and image processing) for the pixels in each individual row, corresponding to the number of active columns. When image sensors are produced, manufacturing defects or yield loss resulting in even a single inoperable or dysfunctional processing data-path may further limit the operable resolution and frame rate.
Image sensors that are operated using an ERS algorithm have inherent bounds on the maximum frame rates that they can achieve while maintaining image resolution and robust imaging capabilities. Such image sensors are also susceptible to manufacturing defects that both increase the costs associated with producing a fully operational sensor and decrease the functionality of an image sensor.
It would therefore be desirable to provide improved image sensors and methods for operating image sensors.